For the lighting of offices and environments destined to working and commercial activity in general, as well as in the case of lighting of spaces destined to the display of articles of commerce such as windows of shops, and finally also for the lighting of particular domestic spaces, frequently use is made of bipolar rails in quality of supports for the several light sources, as example orientable spot lights. At the interior of these rails there are located a phase conductor, a neutral conductor and possibly a ground connector and these are arranged in order to allow an easy lock-in of the lamp holder or lamp holders correspondingly shaped. The rails in question may carry a number of light sources, according to their electrical dimensioning, that are destined to contemporaneous operation if the rail has a single phase conductor. When the need arises of selectively actuating various light sources installed on the same rail, the rail must contain a number of phase conductors corresponding to the number of the loads or groups of loads that one may wish to operate independently. All this requires a more complex structure which is consequently more costly, both with respect to the rail and with respect to the lamp holder, and finally to the electric supply plant of the rail itself.
The aim of the present invention is to render possible the use of bipolar rails also when are located thereon loads, in particular, light sources, which have to operate in an independent way.